A significant shortcoming in current radio systems and in those that are being developed is the limited amount of radio resources available. The number of radio frequencies is restricted and they are distributed among various systems and operators. Numerous different solutions have been created to solve this problem.
Previously developed radio systems meant for public use are based on circuit-switched technology. In systems implemented according to this technology, a specific channel is reserved for the connection between the devices involved, the connection being available to the devices for the entire duration of the connection, irrespective of whether there is traffic on the channel all the time or not. This solution has been sufficient for systems relaying primarily speech. However, with increasing telecommunications needs, transmission connections are used for transmitting data. The traffic relayed on data connections is often highly bursty, i.e., at times data is transferred in large amounts and a lot of transmission capacity is needed on the channel, whereas occasionally the traffic load on the channel is low. From the point of view of capacity deployment, packet-switched transmissions are an extremely good solution for these connections. In packet-switched connections, the channel is not allocated to the terminals for the entire duration of the connection, but the channel is only allocated when data needs to be transferred. Consequently, diverse radio systems employing packet-switched service have been developed, at least some of the connections between the terminals being established using a packet protocol. Among these systems are GPRS (General Packet Radio system) and its enhanced version EGPRS (Enhanced General Packet Radio System).
Since various data services are available and they have differing data transmission needs, many systems include the possibility to establish connections of varying capacity. Moreover, many systems involve diverse terminals which may be provided with highly varying data transmission properties and capability to deploy the resources of the system. For example, different equipment and data transfer capacity is needed for transferring speech, written communications or video. In addition, there may be devices that can only use specific frequency ranges and others that can utilize all the frequencies reserved for the network. Consequently, when a radio connection is to be established, the system should know the type of the terminal that needs the connection and the data transmission capacity. There are also networks that may have different packet system protocols available, such as the GPRS and EGPRS, and depending on its characteristics, the terminal can use one or the other.
In prior art solutions a terminal that needs to transmit data in packet format contacts the network and informs that it wishes to establish a connection and, at the same time, it informs what kind of a terminal it is, i.e., the radio path characteristics it has. These characteristics include for example the frequencies the device needs for communication, and the transfer modes of different capacities that the terminal can utilize. A prior art signalling for connection establishment is illustrated in FIG. 1. The Figure shows the essential parts of messages sent by different devices. The messages sent by the network part are marked with DL (downlink). A terminal sends a CR (Channel Request) 100 to the network part of the system. The network part allocates one radio block to the terminal and responds by sending the terminal an IA (Immediate Assignment) 102. The terminal uses the allocated radio block to send a PRR (Packet Resource Request) 104. This request comprises information about the terminal's radio path characteristics. The network part allocates one or more channels to the terminal and responds by sending a new response 106 where the reserved channels are informed to the terminal. The terminal then starts to send data 108. In the example of FIG. 1, the terminal uses three parallel 110-114 channels.
One of the drawbacks of the above method is that it is not possible to know whether the terminal needs GPRS (General Packet Radio System) or EGPRS (Enhanced General Packet Radio System) resources. Another problem is that one allocated block is sufficient for sending one control message, but one control message is not always enough for relaying the radio characteristics of the terminal. Consequently, a terminal having diversified characteristics does not necessarily receive appropriate resources.
The signalling that takes place before data transmission is a multi-step process, i.e., it comprises a plural number of steps depending on the amount of data to be transferred and the amount resources available. When GPRS is used, the signalling can take place either on a PCCCH (Packet Common Control Channel) or a CCCH (Common Control Channel), but with EGPRS only PCCCH can provide efficient signalling. This causes delay in the transmission of the signal and yet the data transmission is not necessarily carried out in an optimal way due to insufficient signalling capacity.